Treatment of natural gas in distribution systems



Dec. 27, 1960 R. l.. HAscHE 2,966,402 TREATMENT OF NATURAL GAS IN DISTRIBUTION SYSTEMS Filed Aug. 26. 1954 1N VEN TOR.

@MWMHM ATTORNEYS `steel'storage cylinders. v expensive, hazardous and requires expensive compressor 2,966,402 TREATMENT F NATURAL GAS IN DISTRI- BU'IION SYSTEMS Rudolph Leonard Hasche, `lohnson City, Tenn., assignor to Carbonic Development Corporation, Johnson City, Tenn., a corporation of Delaware Filed Aug. 26, 1954, Ser. No. 452,423 9 Claims. (Cl. 425-196) The present invention describes a new and improved process for the separation and storage of natural gas constituents for later use in distribution systems. More particularly, it comprises a new method for a public or private consumer of natural gas to recover and store heavier constituents of natural gas during a period of ample supply, such as in the summer season, to furnish a-reserve supply during the winter season or period of .short supply or interruption of natural gas service.

With continued growth in the use of natural gas throughout the world, and particularly in the United States, the peaks in demand in the heating season in the winter have made more acute the problem of building up reserves for peak periods. The problem is partly met by increasing the amount of natural gas sold by the distributors on an interruptible basis. This method causes inconvenience particularly to industrial users requiring them, in many cases, to provide their own stand-by facilities and also leads to loss in revenue to the natural gas distributor since it requires a lower price to compensate for the interruption in service.

There are several other partial solutions to the problem of bridging over periods of peak demands for natural gas. One of the methods which can be used in certain locations is to pump excess gas available in the summer season into underground storage structures. This method has been used in a limited number of locations where underground storage basins, such as depleted oil or -gas fields, exist. However, this solution is not universally available or entirely satisfactory due to losses `and contamination. Another method is to pump excess natural gas in the summertime into very high pressure However, this method is very equipment. Still another method which was attempted was to liquefy natural gas and store it at low temperature. A fatal accident at Cleveland several years ago has stopped the development of this method. Stillanother method is to provide stand-by sources of peak shaving or stand-by supply. This method entails the use of equipment for making oil gas that can be diluted with air, reforming units operating on propane or natural gasoline or propane-air systems. All of these lattersystems require the purchase of auxiliary `.supplies of .hydrocarbon feed stocks at a lluctuating market price.

Extra operating staffs, to be maintained for emergency operation, are also required.

The present invention has for its primary object the provision of an economical, self-contained method for operating a gas distribution plant whereby there is re covered from natural gas supplied to theplant `during periods of normal or minimum demand, as in the vsummertime, the heavier and higher molecularrweight constituents, such as ethane, propane, butanes, pentanes and higher hydrocarbons in liquid form, for storing the liquefied product so obtained at a comparatively low pressure which is automatically maintained, and for returning the stored product in gaseous form to the distribution system in periods of peak demand or as asole `supply of gas in case of interruption of the primary source of supply.

A further object of the invention is to carry out the process, as above referred to, without the use of sources of heat or power not inherently present in the gas plant.

Yet another object of the invention is to provide a reserve supply of gas for use during periods of peak demand at a lower cost for investment and operation than is possible by methods known to the prior art.

My invention involves the separation and liquefaction of heavier constituents of natural gas, i.e., ethane and hydrocarbons boiling at temperatures higher than ethane, employing as the refrigeration requisite to etect such liquefaction low temperature obtained by the adiabatic expansion of gas from a transmission line pressure to an intermediate pressure generally corresponding to that employed in the gas distribution line. The cold, liquefied product is stored at the pressure of the distribution line. The cold, adiabatically expanded stripped gas from which the liquefied product is separated, is passed in heat exchange relationship with the high pressure gas from the transmission line to cool such gas and to effect condensation of the heavier constituents thereof.

This invention is addressed primarily to a method and system for use in a gas plant which obtains fuel gas, such as natural' gas, from a high pressure pipe line or transmission line, and converts such gas to a substantially lower pressure for distribution in a distribution line to ultimate consumers.

Throughout this specification, the term transmission line is used to referto the high pressure pipe line from lwhich the gaseous product is received by the distribution plant. Similarly, transmission line pressure refers to the pressure of the gas in the transmission line, normally about 400 to 1000 pounds Yper square inch. ln like manner, the term distribution line refers to the line by which the plant distributes its heating gas product at a substantially lower pressure to ultimate consumers. The term distribution line pressure, accord- `inglyrerfers to the pressure of the product heating gas in the distribution line, normally .a pressure of about 50 to 200 pounds per square inch. l'

A particular advantage of the invention resides in the storageof the cold, liqueiied heavier constituents under the distribution line pressure. This liqueiied product is maintained at a low temperature in equilibrium with the distribution line pressure. The liquid product, which is a mixture of ethane, propane, butanes, pentanes and higher hydrocarbons (together with some dissolved methane which is discharged into the transmisison line by an vinherent degassing which is described hereinafter), if allowed to come to room temperature in a sealed vessel would exert a pressure of over A500 pounds per square inch and would, therefore, require expensive storage tanks together with elaborate safety precautions. However, in my process the cold liquid formed in the system is substantially continuously, at least during periods of normal or minimum demand, flowed into the storage vessels to make up for heat loss through the walls of the vessels, and if such cold liquid is insufficient to maintain the liquid in the storage vessels at equilibrium temperature,small amounts of liquid in the storage vessels will automatically boil ott into the distribution line and thereby supply additional refrigeration. Methane, which is dissolved in the liquid product at the primary condensa- `tion pressure,is released in the storage vessels and may tem, as ,explained nin detail (hereinafter. V Itmwillube appreciated that the system may be operated intermittently as well as continuously, refrigeration supplied by the boiling of the liquid product in the storage vessels being sufficient alone to maintain equilibrium conditions for a reasonable period of time. The system of this invention, including the method and apparatus, is integral with the transmission and distribution of gas lines and with conventional gas plant equipment. The system provides maximum safety coupled with automatic control.

My invention has almost universal application for municipal gas distribution systems, and gas distribution systems operated independently by large industrial consumers where natural gas is obtained from cross-country transmission lines. In general, natural gas in crosscountry transmission lines is piped under high pressure and arrives at the municipal or industrial gas distribution system at pressures of from about 400 to 1000 lbs. per square inch gauge. The distribution plant is operated to reduce the pressure of the gas in the pipe line to a distribution line pressure which is normally in the range of from about 50 to 200 lbs. per square inch gauge. The reduction in pressure is carried out by pressure reducing valves in free expansion.

According to my invention, the energy residing in the gas while at transmission line pressure is utilized by adiabatic expansion in an expansion engine of conventional design, and the refrigeration thus obtained is employed to eifect condensation of the heavier constituents of the gas. A separation normally of at least about 5% of the total heating value of the natural gas is thus effected, while the heating Value of the stripped gas from which the liquefied material is separated on a cubic foot basis is reduced to a lesser extent, since the heavier constituents p of the gas are characterized by a higher heating value per cubic foot than the lighter constituents, such as methane. For example, if 7% of the total heating value of a natural gas is removed by condensing out one-half of the ethane in the gas, which originally contained 10% ethane and about 90% methane, the heating value of the gas on a cubic foot basis would be reduced from 1078 B.t.u./cf. to 1040 B.t.u./cf. or only about 3.8%. Similarly, if the natural gas contained propane and butane, the removal of an equal percentage of the total heating value of the gas by the condensation and separation of these heavier constituents would result in a substantially lesser reduction of the heating value per cubic foot of the stripped gas.

The features and method of operation of my invention will be best understood by description and reference to the single ligure, which is a diagrammatic representation of one form of equipment which may be used in the practice of the invention.

Natural gas supplied from a high pressure transmission line, not shown, at a pressure of about 1000 lbs. per square inch to about 400 lbs. per square inch enters the system by pipes 1, 2 and 3, valve 4, and pipe 5, and is dehydrated by passage through dehydrator 6, which is of conventional design, and may appropriately contain silica gel as a dehydrating agent. The dehydrated gas, still at substantially the transmission line pressure, then flows through pipe 7, valve 8, and pipes 9 and 10 into the tube side of the heat exchanger 11, which is of the standard tube and shell design. Valves 12, 13 and 18 are closed, and valve 14 operates to foreclose passage of the gas through the pipe 40.

Dehydrators of the type above referred to become fully charged or loaded with moisture and must be reactivated as by passing hot air therethrough and thereafter cooling. In the practice of this invention, suitable cooling can be effected by passing a portion of the cooled, dry natural gas obtained by separation of the liquid fraction formed in the heat exchanger therethrough. Since such dehydrators cannot be continuously operated, a systeml of two dehydrators for alternate operation isemployed. To this end, a second dehydrator 15, similar to dehydrator 6, is

provided. The dehydrator 15 is connected to the pipe 3 by valve 12 and pipe 16, and to the exchanger 11 by pipe 17, valve 18, pipe 9 and pipe 10. When it is desired to reactivate the dehydrator 6, valves 4 and 8 are closed and valves 12 and 18 are opened. Gas from the transmission line then enters the system through pipes 1, 2 and 3, valve 12, and pipe 16, and then is dehydrated by -passage through the dehydrator 15. From the dehydrator 15, the dry gas ows through pipe 17, valve 18, and pipes 9 and 10 into the heat exchanger 11.

The dry natural gas, still at transmission line pressure, passes downwardly through the tube side of the heat exchanger 11 and is thereby cooled to a temperature normally of at least about 75 F. and preferably from about F. to about 130 F. to effect condensation of the heavier constituents of the gas including ethane, propane, butanes, pentanes and heavier hydrocarbons. The liquefied material so produced is collected in the pot 19 at the bottom of the heat exchanger 11. The cold stripped gas from which the liqueed product is separated flows through pipe 19a into the expansion engine 20, which may be of any conventional design, wherein the cold gas is expanded adiabatically doing external work, thereby cooling the gas to a temperature of about F. to about 250 F., preferably approximately 200 F., and lowering the pressure of the gas to distribution line pressure of about 150 to about 250 lbs. per square inch, preferably approximately 200 lbs. per square inch. The final temperature of the expanded gas depends upon the degree of the expansion in the expansion engine. In a typical case, the dry gas is expanded from a transmission line pressure of about 600 lbs. per square inch to a distribution line pressure on the order of about 200 lbs. per square inch gauge to provide an expanded gas at a temperature of about 200 F. rlhe expanded gas at the low temperature above referred to exits from the expansion engine through the pipe 21 and is passed into the shell side of the heat exchanger 11 where it is passed in heat exchange relationship with the incoming dry gas from the transmission line. The expanded gas is warmed by the aforementioned passage through the heat exchanger to a` temperature of from about 15 F. to about 50 F., pref-V erably approximately 30 F., below the temperature of the incoming gas which enters the heat exchanger through the pipe 10. The expanded, stripped gaseous product then exits from the heat exchanger through the pipe 22 and ows through the valve 23 into the distribution line 24 for transmission to ultimate consumers.

The liquefied material which is recovered in the pot 19 is continuously transferred, preferably automatically, by conventional ow control means shown at 25, through valve 26, pipe 27, valve 28 and pipes 29, 30 and 31 to insulated storage tanks 32 and 33. There may be as many storage tanks as desired or required. Pipes 34 and 35 are provided at the top of the storage tanks 32 and 33 and are connected through pipe 36 and valve 37 to the main distribution line 24. Normally, the valve 37 is in open position so as to maintain the liquid in the storage tanks 32 and 33 under the pressure of the distribution line. It will be apparent that the temperature of the liquid in the tanks 32 and 33 will be governed by the distribution line pressure, the composition of the liquid in the tanks, and the heat flow from the outside into the liquid in the tanks. The liquid flowing into the storage tanks 32 and 33 from the above described liquefaction operation will normally be at a temperature in the neighborhood of 200 F. However, in the storage tanks heat ow from the sur- 'roundings will gradually raise the temperature of the liquefied product until pressure equilibrium conditions are established between the product in the storage tanks 32 and 33 and the distribution line pressure. The ultimate composition of the liquid in the storage tanks 32 and 33 will depend upon the composition of the original gaseous l material which is treated in accordance with the invention and the degree of expansion of the stripped gas which `-is carriedfout in the expansion-engine. .expansion in turn is a function Aoflthe dilerence-lnpresgas can be drawn through the pipe .sor 39, which is of conventional design, where it is comgas is raised to an extent greater than 'The degree of sure between the transmission line and the distribution line. The greater the ratio of transmission line pressure to the gas distribution line pressure and consequently .-g

the degree of expansion in the engine or turbine, the greater the refrigeration obtainable andconsequently the recovery of hydrocarbons heavier than methane. The

examples hereinafter set forth illustrate the effect ofthe foregoing factors.

In the condensation of ethane, propane, butanes, pen- .tanes, and heavier hydrocarbons in theheat exchanger` 1l,

some methane will be contained in the liquid due to solubility etfect. However, in passing through the -valve 26 `an expansion occurs from the transmission line pressure `to the distribution line pressure, and consequently the methane will be released from the liquid in thestorage tanks 32 and 33 and will ow back into the main transmission line. In other words, in the tanks 32 and 33 and in the course such tanks, degassing occurs thereby` stabilizing the liquefied product.

The methane released in the tanks 32- and 33 by reduction in pressure will normally contain substantial amounts of ethane. When the valve 37 is throttled, this enriched l38 into the comprespressed to the transmission line pressure-and returned to the separation unit through the pipe A40 and the valve 14. The valve 14 is of a differential pressure type, such as to preclude flow of the gas contained in the pipe 2 backwards through the pipe 40. The power required for the recompression is supplied by the expansion engine 20 which is connected in a suitable, conventional meansto the comk pressor 39.

The automatic pressure control, safety and economic advantages of the separation storage and stand-by reserve of the process described in this invention are apparent.

VIf the separation unit isclosed down, valve 28 is closed, and the storage tanks will be maintained lat the pressure of the distribution system. Heat flow with the storage system will lead to vaporization of liquid hydrocarbons to maintain the temperature, and the vaporizedproduct will automatically pass into the distribution system without manual or instrumental control. separation unit, liquid is again supplied to make up for the vaporization during the shutdown and continuous operating equilibrium is reestablished.

The above description has dealt with the operation -and separation of the storage procedures which comprise one part of the invention. The operation of this system will be carried out during the larger part of the year, during the spring, summer and fall, when the demand for gas can be readily met by the transmission line. Now, during the colder months when the demand exceeds the supply, or at least exceeds the demand load contracted for by the municipal or industrial plant, the reserve supply can be drawn upon. To this end, valve 41 is opened and the liquid is fed through pipe 42, pump 43, andpipe 44 `to vaporizer 45. If the demand `is not large, the vaporized product can be fed directly into the distribution line through pipes 46 and 47, valve 48 and pipe 49. It' the demand is so great that the heating value of the natural desired, valve 48 is closed and the valves 50 and 53 are opened, thereby allowing the vaporized product tobe mixed with air or otherwise reformed to lower the heating value, for example, to approximately 1050.B.t.u./cubic foot in a standard apparatus indicated at 51, the gas'llow being-,through the pipe 46,.the valve 50, the reformer 51, the .pipe -52,A

and the valve S3, to the distribution line 24.

In the case when heavy withdrawalis 4made at vpeak demand, there is no occasion to .operate the-.separation unit. Accordingly, .valves 28 and .23., are closed and the main jpressurereducing valve V1.3; is :opened between the of transmission of -the liquid product to Upon restarting of the transmission line transmission-and distribution lines,. sovthat the separation unit is by-passedfrom the gas system.

The following examples will illustrate the practicerofthe invention, but the invention is not restricted to lthe examples.

Example l A natural gas obtained from a cross-country transmisvsion line was introduced into the separation system of this invention at the transmission line pressure of 600 lbs. per square inch gauge. The inlet composition of the natural gas was as follows:

This gas was passed through thepipes 1, 2 and 3, valve 4,'and pipe 5, and was dehydrated in the dehydrator 6. After dehydration, the gas was passed through the pipe 7, valve 8, pipes 9 and 10 into heat exchanger llwhere it was cooled toa temperature of approximately l30 F. At the time of entry into the heat exchanger, the gaswas at a temperature of about 80 F. The -cooling of the gas in the heat exchanger resulted in the condensation of a liqiud product comprising ethane and the hydrocarbons boiling higher than ethane which are present in natural gas, which liquid product contained in solution some methane and which was collected in the pot 19 at the bottom of the heat exchanger 11. The composition of the gas obtained by vaporizing liquid product was:

Vol. Percent The liquid product was equivalent to 6.8% of the total heating value of the inlet natural gas, while the heat- I ing value of the gas per cubic foot was reduced only :from 1051 to 1010 Blu/cubic foot. The caloric-value .of the gas obtained by vaporizing the liquid product was 2241.B.t.u./cubicfoot. The stripped,- gas from which the liquid product was separated iiows through pipe1-9a into expansion engine 2l), where it was expanded from z the inch gauge to a pressure of about inch gauge which corresponded to pressure. After the expansion, ture of about 200 F. This cold expanded gaswas passed through pipe 21 upwardly through the shell portion of the heat exchanger 11 to effect cooling ofthe incoming natural gas and was thereafter withdrawn from the heat exchanger through pipe 22 and valve 23 .into the main distribution line 24. The temperature of the expanded gas at the time of entry into the pipe 22 was about 30 F. below the temperature of the incoming dehydrated gas product.

The liquid product collected in the pot 19 was automatically transferred by oat control 25 through the valve 26, pipe 27, valve 2S, and pipes 29, 30 aud 3&1 into storage tanks 32 and 33. By means of pipes 34, 35 and '36, and open valve 37, the liquid in storage tanks 200 lbs. Vper square the distribution ,line the gas was at a tempera- '32 and 33 was maintained'at equilibrium with thepressure Yin the gas distribution line 24. A 'continuousllow of the cold product-lfrornv'the pot 419 compensates Vv'for pressure of about .600 lbs. per Square heatiiow from the surroundings into the tanks 32 and 'distribution line pressure. Methane contained in the liquid collected in the pot 19 passes ott through the pipes 34, 35 and 36, and valve 37 into the distribution line 24.

In one method of Voperating the invention, valve 37 may be throttled and methane, which contains a substantial portion of ethane, is withdrawn through the pipe 38, compressed in the compressor 39, and conducted through pipe 40 and valve 14 to the pipe 2 where it is reintroduced into the system.

An alternate method of operation is to absorb the work done -by the expander by generating electric power or compress another source of gas.

The foregoing method of operation is carried out during periods of normal or other than peak demand. In periods of peak demand, when it is necessary to supplement the supply of natural gas obtainable by the plant,

-the liquid product in the tanks 32 and 33 is withdrawn through the pipes 29, 30 and 3-1, the valve 41, pipe 42 and passed by the pump 43 through pipe 44 into the vaporizer 45.

Alternatively, the product may be passed into the distribution line from the vaporizer through pipes 46 and 47, valve 48, and pipe 49, valve t) being closed.

If the demand is excessive, it may be desirable to reform the vaporized gaseous product before introduction into the transmission line. rIhis is effected by closing the valve 4S and passing the vaporized product obtained from the vaporizer 45 through the pipe 46, valve S0, reformer 51, the pipe 52, and the valve 53 into the distribution line 24.

Example 1l The process as described in Example I is repeated with the exception that in this instance the natural gas employed has an inlet composition as follows:

Percent Methane 81.97 Ethane 10.00 Propane 3.25 Butanes .6l Pentanes plus .24 Nitrogen 3.93

Total 100.00

Methane 9.2 Ethane 21.4 Propane 55.3 Butanes 11.1 Pentanes plus 3.0

Total 100.0

The caloric value of the gas obtained by vaporizing the liquid product collected in the pot 19 was about 2362 B.t.u./cubic foot.

Example III The process of Example I was repeated with the exception that in this instance the gas was supplied at a transmission line pressure of about 1000 lbs. per square inch which was expanded to a distribution line pressure 8 of about lbs. per square inch. This resulted in the presence of some additional methane in the liquid product collected in the pot 19, but the results were otherwise similar to those described in Example I.

Example 1V The process of Example I was repeated with the exception that in this instance the gas was supplied to the system at a transmission line pressure of 400 lbs. per square inch and was expanded to a distribution line pressure of about 50 lbs. per square inch. The results were analogous to those described 4with reference to EX- ample I.

While this invention has been described particularly with reference to natural gas, it is applicable to the treatment of other forms of heating gas which are conventionally supplied to gas distribution plants. Various forms of synthetically produced or reformed gas can be distributed in accordance with the method of this invention.

While the invention has been herein described particularly with reference to storing the liquefied gaseous product under essentially the distribution line pressure, it will be appreciated that-it is within the purview of the invention to store the liquid product under a pressure intermediate the transmission line pressure and the distribution line pressure. Such intermediate pressure could, for example, be effected if the stripped gas were issued from the heat exchanger at a pressure in excess of that at which it is ultimately passed into the transmission line and the liquid product was stored under equilibrium with the gas at such intermediate pressure.

I claim:

1. A method of operating a plant for converting a high pressure natural gas supplied by a transmission line to a substantially lower pressure heating gas and for distributing said heating gas to consumers with a minimum of interruption, which comprises: (l) withdrawing said natural gas under transmission line pressure from the transmission line by which said gas is supplied to said plant; (2) Vcooling said gas while under substantially transmission line pressure to form (a) a condensed liquid fraction comprising predominantly ethane and hydrocarbons boiling at a temperature higher than ethaue, and (b) a gaseous fraction comprising predominantly methane; (3) adiabatically expanding said gaseous fraction to an extent requisite to effect said cooling in step (2); (4)

Vpassing said cold expanded gaseous traction in heat exchange relationship with said natural gas to effect the cooling in step (2) and thereafter passing said expanded gas into the distribution line of said gas plant; (5) substantially continuously conducting said liquid fraction in the liquid state to at least one storage vessel maintained in communication with the distribution line during operation of the said plant, and wherein said liquid fraction is maintained at a pressure equal to that of the expanded gas in said distribution line; and (6) during periods ot' peak demand vaporizing said liquid product and introducing the gaseous material so obtained into said distribution line for use as a heating gas; substantially all of said liquid products ultimately being introduced into the distribution system.

2. The process of claim l wherein said gaseous fraction is adiahatically expanded in step (3) to a pressure corresponding to the distribution line pressure maintained by said gas plant.

3. The process of claim l wherein said natural gas when withdrawn from said transmission line is under a transmission line press-ure of from about 1000 to about 400 lbs. per square inch gauge, wherein said gas is cooled in step (2) to -a temperature of not more than about 75 F., and wherein said gaseous fraction is adiabatically expanded in step (3) to a pressure of from about to about 250 lbs. per square inch and thereby cooled .to atemperatureLof about 150 F. to about 250 F.

Wert.

4. A method of operating a plant for converting a high pressure natural gas supplied by a transmission line to a substantially lower pressure heating gas and for distributing said heating gas to consumers with a minimum of interruption, which comprises: (1) withdrawing said natural gas under a transmission line pressure of about 400 to about 1000 lbs. per square inch from the transmission line by which said gas is supplied to said plant; (2) cooling said gas while under substantially transmission line pressure to a temperature of about -90 to about 130 F. to form (a) a condensed liquid fraction consisting essentially of ethane and hydrocarbons boiling at a temperature higher than ethane, said condensed liquid fraction representing at least about of the total heating value of said natural gas, and (b) a. gaseous fraction consisting essentially of methane; (3) adiabatically expanding said gaseous fraction to a pressure of about 150 to about 250 lbs. per square inch thereby cooling said fraction to a temperature of about -150 F. to about -250 F.; (4) passing said cold expanded gaseous fraction in heat exchange with said natural gas to effect cooling in step (2) and thereby warm said gas to a temperature of from about F. to about 50 F. below the temperature of the natural gas when withdrawn from said transmission line; (5) passing said expanded warm gas into the distribution line of said gas plant; and (6) conducting said liquid fraction in the liquid state to at least one storage vessel maintained in uid communication with the distribution line during operation of the said plant and storing said liquid fraction in such vessels at a pressure equal to that of the said expanded gaseous fraction in said distribution line.

5. A method of operating a plant for converting a high pressure natural gas supplied by a transmission line to a substantially lower pressure heating gas and for distributing said heating gas to consumers with a minimum of interruption, which comprises: (1) withdrawing said natural gas under transmission line pressure from the transmission line by which said gas is supplied to said plant; (2) cooling said gas while under substantially transmission line pressure to form (a) a condensed liquid fraction comprising predominantly ethane and hydrocarbons boiling at a temperature higher than ethane, and (b) a gaseous fraction comprising predominantly methane; (3) adiabatically expanding said gaseous fraction to an extent requisite to effect said cooling in step (2); (4) passing said cold expanded gaseous fraction in heat exchange relationship with said natural gas to effect the cooling in step 2) and thereafter passing said expanded gas into the distribution line of said gas plant; (5) substantially continuously, at least during periods of ample supply of said natural gas, conducting said liquid fraction in the liquid state to at least one storage vessel maintained in fluid communication with the distribution line during operation of the said plant, and wherein said liquid fraction is maintained at a pressure equal to that of the gas in said distribution line; and (6) during periods of peak demand vaporizing said liquid product and introducing the gaseous material so obtained into said distribution line for use as a heating gas; substantially all of said liquid products ultimately being introduced into the distribution system.

6. The process of claim 5 wherein said gaseous fraction is adiabatically expanded in step (3) to a pressure substantially corresponding to the distribution line pressure maintained by said gas plant.

7. The process of claim 6 wherein said vaporized product in introduced directly into said distribution line.

8. A method for operating a plant for converting a high pressure natural gas supplied by a transmission line to a substantially lower pressure heating gas and for distributing said heating gas to consumers with a minimum of interruption, which comprises: 1) withdrawing said natural gas under transmission line pressure from the transmission line by which said gas is supplied to said plant; (2) removing moisture from and cooling said gas while under substantially transmission line pressure to form (a) a condensed liquid fraction comprising predominantly ethane and hydrocarbons boiling at a temperature higher than ethane, and (b) a gaseous fraction comprising predominantly methane; (3) adiabatically expanding said gaseous fraction to an extent requisite to eifect said cooling in step (2); (4) passing said cold expanded gaseous fraction in heat exchange relationship with said natural gas to effect the cooling in step (2) and thereafter passing said expanded gas into the distribution line of said gas plant; (5 substantially continuously, at least during periods of ample supply of said natural gas, conducting said liquid fraction in the liquid state to at least one storage vessel maintained in fluid communication with the distribution line during operation of the said plant, and wherein said liquid fraction is maintained at a pressure equal to that of the gas in said distribution line; and (6) during periods of peak demand vaporizing said liquid product and introducing the gaseous material so obtained into said distribution line for use as a heating gas; substantially all of said liquid products ultimately being introduced into the distribution system.

9. A method of operating a plant for converting a high pressure natural gas supplied by a transmission line to a substantially lower pressure heating gas and for distributing said heating gas to consumers with a minimum of interruption, which comprises: 1) withdrawing said natural gas under transmission line pressure from the transmission line by which said gas is supplied to said plant; (2) cooling said gas while under substantially transmission line pressure to form (a) a condensed liquid fraction comprising predominantly ethane and hydrocarbons boiling at a temperature higher than ethane, and (b) a gaseous fraction comprising predominantly methane; (3) adiabatically expanding said gaseous fraction to a pressure substantially corresponding to the distribution line pressure maintained by said gas plant to effect said cooling in step (2); (4) passing said cold expanded gaseous fraction in heat exchange relationship with said natural gas to effect the cooling in step (2) and thereafter passing said expanded gas into the distribution line of said gas plant; (5) substantially continuously, at least during periods of ample supply of said natural gas, conducting said liquid fraction in the liquid state to at least one storage vessel maintained in fluid communication with the distribution line during operation of the said plant and wherein said liquid fraction is maintained at a pressure equal to that of the gas in said distribution line; and 6) during periods of peak demand Vaporizing said liquid product, reforming said Vapor to reduce the heating value thereof and introduce the gaseous material so obtained into said distribution line for use as a heating gas.

References Cited in the tile of this patent UNITED STATES PATENTS 337,668 Dalzell Mar. 9, 1886 1,626,345 Le Rouge Apr. 26, 1927 1,772,101 Knapp Aug. 5, 1930 2,082,189 Twomey June 1, 1937 2,090,163 Twomey Aug. 17, 1937 2,265,558 Ward Dec. 9, 1941 2,530.602 Dennis Nov. 21, 1950 2,640,768 MacSporran June 2, 1953 2,677,945 Miller May 11, 1954 2,696,088 Twomey Dec. 7, 1954 2,716,332 Haynes Aug. 30, 1955 2,719.080 Schmidt Sept. 27, 1955 2,740,701 Tenney Apr. 3, 1956 2,765,635 Redcay Oct. 9, 1956 FOREIGN PATENTS 360,487 Great Britain Nov. 9, 1931 

1. A METHOD OF OPERATING A PLANT FOR CONVERTING A HIGH PRESSURE NATURAL GAS SUPPLIED BY A TRANSMISSION LINE TO A SUBSTANTIALLY LOWER PRESSURE HEATING GAS AND FOR DISTRIBUTING SAID HEATING GAS TO CONSUMERS WITH A MINIMUM OF INTERRUPTION, WHICH COMPRISES: (1) WITHDRAWING SAID NATURAL GAS UNDER TRANSMISSION LINE PRESSURE FROM THE TRANSMISSION LINE BY WHICH SAID GAS IS SUPPLIED TO SAID PLANT, (2) COOLING SAID GAS WHILE UNDER SUBSTANTIALLY TRANSMISSION LINE PRESSURE TO FORM (A) A CONDENSED LIQUID FRACTION COMPRISING PREDOMINANTLY ETHANE AND HYDROCARBONS BOILING AT A TEMPERATURE HIGHER THAN ETHANE, AND (B) A GASEOUS FRACTION COMPRISING PREDOMINANTLY METHANE, (3) ADIABATICALLY EXPANDING SAID GASEOUS FRACTION TO AN EXTENT REQUISITE TO EFFECT SAID COOLING IN STEP (2), (4) PASSING SAID COLD EXPANDED GASEOUS FRACTION IN HEAT EXCHANGE RELATIONSHIP WITH SAID NATURAL GAS TO EFFECT THE COOLING IN STEP (2) AND THEREAFTER PASSING SAID EXPANDED GAS INTO THE DISTRIBUTION LINE OF SAID GAS PLANT, (5) SUBSTANTIALLY CONTINUOUSLY CONDUCTING SAID LIQUID FRACTION IN THE LIQUID STATE TO AT LEAST ONE STORAGE VESSEL MAINTAINED IN COMMUNICATION WITH THE DISTRIBUTION LINE DURING OPERATON OF THE SAID PLANT, AND WHEREIN SAID LIQUID FRACTION IS MAINTAINED AT A PRESSURE EQUAL TO THAT OF THE EXPANDED 